Various technologies have been developed utilizing techniques in which fluids are ejected from a reservoir by focused acoustic energy. An example of such technology is typically referred to as acoustic ink deposition which uses focused acoustic energy to eject droplets of a fluid, such as ink, from the free surface of that fluid onto a receiving medium.
Generally, when an acoustic beam impinges on a free surface, e.g., liquid/air interface, of a pool of liquid from beneath, the radiation pressure will cause disturbances on the surface of the liquid. When the radiation pressure reaches a sufficiently high level that overcomes the surface tension of the liquid, individual droplets of liquid may be ejected from the surface.
However, many different factors may arise which can interfere with the droplet ejection and resulting droplet trajectory. For instance, care must be taken to accurately direct the acoustic beam to impinge as exclusively as possible on the desired lens which focuses the acoustic beam energy. Some undesirable effects of the acoustic beam impinging other than on the desired lens include insufficient radiation pressure on the liquid surface, lens cross-talk, and generation of undesirable liquid surface disturbances. Each of these effects may result in the loss or degradation of droplet ejection control.
A further problem related to liquid surface disturbances include surface waves affecting the surface planarity. These waves result in deviations of the free surface from planar and alter the location of the surface relative to the focal point of the lens, thereby resulting in degradation of droplet ejection control. The result of this is a varying angle of droplet ejection.
Droplets will tend to eject in a direction normal to the liquid surface. For optimum control of placement of the droplet onto an opposing target medium, conventional methods have included maintaining ejection angles of the droplets at a predetermined value, generally perpendicular to the local angle of the surface of the opposing target medium. Accordingly, attempts have been made to maintain a liquid surface parallel to the target medium. Surface disturbances will vary the local surface angle of the liquid pool, especially over the acoustic lenses. This typically results in drop ejection at varying ejection angles with a consequent loss of deposition alignment accuracy and efficiency.
Other conventional methods have included increasing the energy required to cause the droplet ejection to account for varying droplet ejection angles; however, this may have adverse effects on droplet size, droplet count, and droplet ejection direction control.
Another conventional method includes varying the transducer size such that illumination outside the lens is minimized. A further method has included increasing the radius of the acoustic lens itself such that the diverging acoustic waves impinge fully on the lens. However, this generally increases the size and cost of the system and is not necessarily efficient in controlling the droplet ejection angles.
Small volumetric liquid droplets moving individually through free space over distances greater than about 100 times their diameter typically have problems repeating the same trajectory and positional orientation. Accordingly, there remains a need for an efficient device and method for effectively controlling, steering, or correcting the trajectories of droplets ejected from a liquid surface such that they are accurately placed on a targeting medium.